The present system relates to a disconnectable mooring system for use in connection with dedicated storage tankers for the transfer of hydrocarbons and in areas where the tanker vessel needs to be disconnected in case of a typhoon or hurricane warnings or when endangered by icebergs.
Prior to the present invention, such systems included a buoyant connector element which is raised and connected to equipment on the tanker. Such mooring systems are known from European Patent Specification 0.059.499 and GB 2.094.738A. In these mooring systems the chains carrying connector body comprises a buoyancy compartment to keep the connector body near or at the surface of the water. In this structure the tanker engages the mooring system at its bow.
Another prior system is shown in U.S. Pat. No. 4,604,961 in which the mooring system includes a buoyant connector which is engaged within a recess through the hull of the floating vessel. The buoyancy of the connector or mooring element is selected so that when it is disconnected from the vessel it sinks to a depth which is spaced above the ocean floor.
In deeper water sites with severe weather conditions requiring heavy anchor chains, the buoyancy compartment must be large to keep the connector body near or on the surface. The practical experience in the application of these systems has shown that during the hook-up operation, whereby the buoyant connector body is slowly pulled up by the vessel, strong lateral swinging motions occur as a result of wave or current effects on this buoyant body. This effect is dependent on the tension force in the pull-in rope and, therefore, becomes more pronounced in deep water applications.
The present invention relates to a semi-permanent mooring system comprising a floating unit or vessel which could have storage capacity, such as a tanker, mooring legs, such as chains or cables, for anchoring the vessel, which legs are connected to a connector body which is rotatably secured about a vertical axis to the vessel and through which connector body conduits extend towards the vessel and into a rotatable pipeline coupling for one or more pipes which coupling is supported by the vessel whereby the connector body can be connected or released from the vessel if such is required for typhoon or iceberg warnings.
An object of the invention is to provide an improved mooring system in which the connector body is nonbuoyant and is supported in the water and is readily retrievable by a floating structure.
Another object of the present invention is to provide an improved mooring system of the type described in which the current and wave action on the connector body during retrieval are reduced.
As used herein, the term nonbuoyant is intended to mean that the connector body will not have sufficient buoyancy to float or to carry any portion of the mooring legs.